Levels inZr90: Theoretical

An attempt is made to describe the seven levels of ${\mathrm{Zr}}^{90}$ below 3.6 Mev in terms of the proton configurations ${\left(2\mathrm{}{p}_{\frac{1}{2}}\right)}^2$, ($2p_{\frac{1}{2}}1g_{\frac{9}{2}}$), and ${\left(1\mathrm{}{g}_{\frac{9}{2}}\right)}^2$. The level positions and the compositions of the two 0+ states are determined for Gaussian and Yukawa forces of various ranges and exchange characters. The experimental data are well reproduced for a reasonable choice of the force parameters, the best fit being obtained with a Serber exchange mixture and a range of about 1.5 fermis. The experimental values of the half-lives of the excited states can also be reconciled with these simple configurational assignments. The most serious discrepancy is in the half-life of the first excited (0+) state, which we calculate to be 1.35×${10}^{-8\mathrm{}}$ sec, as compared to the observed value of (6.0±1.5)×${10}^{-8\mathrm{}}$ sec. The remaining discrepancies in the energies and half-lives are in the direction of the effects produced by a slight deformation of the ${\mathrm{Sr}}^{88}$ core.